This invention relates to a device for interconnecting two electronic components with large number of individual connections that can be easily disconnected and reconnected, can accommodate surface irregularities and thermal expansion/contraction between the components. A large number implies thousands.
As the circuit density increases on the chip, the number of input and output signals to these chips also increases. These i/o are compressed into a small area to assembly the chip density and are used for the chip to communicate to other nearby chips or to other components in the system. The chips can be attached to a ceramic device as shown in U.S. Pat. No. 3,921,285, issued to Krall and assigned to the present assignee. This patent shows a rigid ceramic chip carrier attached to silicon integrated chips. This ceramic carrier is usually attached to a printed circuit board which integrates a large number of these chips contained on ceramic chip carriers. On systems with multiple processors, usually multiple ceramic carriers are used to allow for performance growth in the customers office by adding additional processors. High reliability is a key and essential criteria for a separable and reconnectable connector for these chip carriers and as a result must be tolerant of dust and mini fibers.
Also when connecting two surfaces, such as the ceramic material and the glass-epoxy. printed circuit board, a significant amount of compliance is required for the glass-epoxy board and must be accommodated by the connector. This is due to the flatness and irregularities inherent in the surfaces of the board and electronic module. The planarity and rigidity of the ceramic is relatively good and as pressure is applied to the edge of the ceramic component to make connection for a plurality of connectors, the glass-epoxy printed circuit board has a tendency to bow as the area array increases. This bowing must be accommodated by the connector. Very large ceramic modules may bow as well if pressures are applied to the perimeter only.
An article titled "High Density Pinless Module Array Connector" by R. Darrow et al, IBM Technical Disclosure Bulletin, Vol. 28, No. 3, page 1079, (August 1985) discloses a connector assembly with wires bent to form a C spring at one end with the other end inserted into the plated through hole of a printed circuit board and soldered. The C spring rests on a plastic housing that supports the force applied by the ceramic module. The density of this connector array is limited by the density of the plated through holes in the printed circuit board and the plastic housing to support the force applied to the C spring by the ceramic module. Density will also be impacted by the C spring shape infringing with the adjacent C spring.
U.S. Pat. No. 4,764,848 issued to Simpson discloses a connector of bent wires which are soldered to both the ceramic chip carrier and the printed circuit board. Each wire has a root at one end and a tip at the other end. The root of each bent wire is attached to the integrated circuit package to form a fixed electrical and mechanical connection. The tip of the bent wire is soldered to a pad on the surface of the printed circuit board. This arrangement provides for strain relief of the connection and mechanically fixes the ceramic device to the board. This disclosure does not provide for an easily removable connector,especially in the customers office.
U.S. Pat. No. 5,248,262 issued to Busacco, et al and U.S. Pat. No. 5,061,192 issued to Chapin, et al discloses a connector assembly with small flat beams attached to a flexible film and contained inside a housing. The small flat beams are copper etched on a polyamide strip, are placed in and extend through the housing, and make contact with pads on circuit members on opposite sides of the connector assembly. This strip of connecting elements is made from several layers of etched or bonded material including a conducting element that contacts the pads, a polyamide backing material, a copper ground plane material and, in the case of U.S. Pat. No. 5,248,262, a stainless steel spring material bonded to but electrically isolated from the copper ground plane. A plurality of the connector elements are contained, and spaced evenly, on the polyamide strip along with the stainless steel spring. The housing contains long slots for the strips to protrude through the surface to make contact with pads on circuit members. The polyamide film retains the contact elements in a single strip and multiple strips make up a connector assembly. Within a single strip, compliance is limited from contact to contact because of the rigidity of the film in that direction. Each contact element has its reacting stresses and strains within its joints set by the amount of its compression and the amount of compression of its adjacent neighbors. As a result, some of the stresses and strains are parallel with the strip and cause shearing to the assembly. To limit the adverse affect of the shearing forces, two precautions must be taken. One is to limited the surface flatness irregularity of the printed circuit board to be within the design limits of the connector assembly. Second, each contact within a strip should be compressed simultaneously, i.e., upon assembly, guides should be used to uniformly force the electronic module upon the array with minimum degree of tilt.
Inherent with the design of having multiple contacts contained within a single strip is that a constant spacing is present between adjacent strips. This limits the degree of optimization of the connector assembly to the application. The tolerances associated with fabricating a single connector strip and bonding to a spring strip may limit the overall length of the strip; and hence, the number of contacts of the connector assembly. The use of connector strips limits the ability to adjust at each contact point the forces applied to the electronic components. These forces caused by the springs will bow the mating surfaces, and depending on the application, may limit the number of contacts allowable. Thus, for high performance applications with high input and output requirements, it is desirable to customize the spring characteristics based on spacial position within the connector array so that module deflections are minimized and number of contacts are maximized.
It is believed that a method of making and assemble a sprint contact element as defined herein which is capable of being used in a separable connector that provides superior electrical characteristics, high reliability, low cost, ease of manufacture, the flexibility to personalize to each application and other advantageous key features below, as contained in this disclosure, advances the state or the art.
It would be highly desirable to have a simple, inexpensive, contact element made from a common source which is extremely reliable with no failures due to delimitations and failed bonds resulting from thermal cycling and aging.
It would also be desirable to have a device to retain these contact elements such that air spacing is provided to adjacent elements for performance and cooling.
It is highly desirable this retainer provide precision alignment via holes and the material can be adjusted for thermal expansion, also with this arrangement each element can individually react to the contact surface.
Also it would be advantageous to personalize the characteristics of each individual contact element and its spacial relationship to the neighboring contact element.
It is also highly desirable that the retainer and contact element assembly accommodate the thermal mismatches between the mating components.
Also it would be essential that the following criteria be met in the disclosure to enhance its flexibility of application:
To improve the packaging density, both sides of the printed circuit board should be utilized which reduces the average wire length and improves the performance of the system.
To provide the maximum density of connections, an area array of these contacts is necessary. Any other configuration would not provide sufficient connections in a given area.
The connector assembly must also exhibit the characteristic of low electrical noise since the application will connect very high speed integrated circuits.
The connector assembly must support large amounts of current in this small area. This leads to a requirement for cooling the connector as power demands are significant.